1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device used in a magnetic disk drive such as a floppy disk drive to control the current supplied to a head to read data from, write data to, and erase data from a magnetic disk serving as a data storage medium, and to reproduce the data read by the head from the magnetic disk.
2. Description of the Prior Art
Such a semiconductor integrated circuit device includes a data reproduction circuit for reproducing the data received from a head, a data output circuit for processing the data output from the data reproduction circuit to make it ready for output, and a circuit for supplying a write/erase current to the head. Conventionally, in such a semiconductor integrated circuit device, during the transition between an operation for erasing data from a magnetic disk to an operation for reading data therefrom, the erase current is first gradually decreased while keeping the data reproduction circuit active, and then, after the lapse of a predetermined length of time, the erase current is reduced to zero. The purpose of keeping the data reproduction circuit active meanwhile is to make the operation of the semiconductor integrated circuit device as a whole stable enough to allow the data reproduction circuit to be deactivated in a power-save mode.
However, since the erase current is reduced to zero while the data reproduction circuit is kept active, the asymmetry of the reproduced data, i.e. the output of the data reproduction circuit, is degraded by the back electromotive force appearing in an erase head, and it takes as long as hundreds of microseconds for the reproduced data to recover its normal characteristics. This means that it takes extra time to achieve recovery from the erase operation to the read operation (i.e. for the reproduced data to recover its normal characteristics and thus become ready for output after the completion of the erase operation). This inconvenience cannot be alleviated without imposing more limitations on the design of the wiring patterns of the circuit board and on the back electromotive force characteristics of the erase head.
Moreover, since the erase current is reduced to zero at the same time that the data output circuit is turned on, the output of the reproduced data can be restarted quickly after the completion of the erase operation, but this causes the data output circuit to output the reproduced data with degraded characteristics.